Power handling capabilities, power-to-lumen efficiencies, and production costs of LEDs have improved over the past few years. Consequently, LED-based ambient lighting has become practical and has begun to compete with compact fluorescent lighting (CFL) technologies as a replacement for power-hungry incandescent lighting.
Challenges to LED lighting include power conversion and heat dissipation requirements. LED arrays typically require low-voltage direct current (DC) and are driven by residential voltage alternating current (AC) to constant current DC power supplies. Light conversion in incandescent bulbs occurs along the filament. Heat from the unconverted power is dissipated from the filament and down through the filament support elements connecting the filament to the base. Light conversion in CFL bulbs occurs via luminescence across a substantial percentage of the interior surface area of the bulb. Heat from unconverted power in the CFL case is generated by the associated mercury vapor discharge process throughout the interior of the bulb and by the ballast circuitry at the base. In the cases of both incandescent and CFL bulbs, waste heat is generated and conducted across relatively large surface areas.
In contrast, a power LED useful for ambient lighting emits light and produces heat across a millimeter-scale semiconductor die surface, resulting in a very high heat flux (watts per unit area). The power efficacy in lumens per watt is much higher for LED lighting as compared to incandescent and is beginning to outpace the efficacy of CFL bulbs. Said differently, LED lighting produces less heat per lumen than the other two technologies. However, the high heat flux resulting from the very small emission surfaces associated with LED dies creates a considerable waste heat removal problem. Consequently, commercially available direct-replacement LED bulbs typically include bulky, complex heat dissipation elements as well as AC to constant current DC internal power supplies. The incorporation of these support apparatus into each LED light bulb currently disadvantages LED lighting's initial cost to performance ratio as compared to that of older technologies.